I really liked the prairies, though not for the roads. There's plenty of gravel though. I liked seeing herds of prong-horn antelope and all kinds of birds of prey.
Lots of cool old buildings and well preserved cars from the 1940's and earlier.
For prairie ideas check out Lornce's Across Canada on a '71 R50/5
And I can dig up some GPS tracks from the prairie portion of my trip